The purpose of this research is to investigate the role of the muscles of mastication in determining the growth and form of the craniofacial skeleton. Emphasis is placed on (a) defining the normal structure and function of the muscles and distribution of bone strain within the craniofacial region as these covary during the growth process; and (b) determining the interrelationships between muscle function, bone strain and craniofacial form by experimental-surgical intervention. Analytical techniques include gross and microscopic anatomy, electromyography, strain gage analysis, analysis of contractile properties and histochemistry.